The present invention relates to a new satellite configuration which permits a three-axes attitude control of the satellite with continuous pointing of one axis to the earth for payload operation.
To date the usual spacecraft configuration comprises a payload and service module pointing to the earth and solar arrays mounted on the north and south faces of the spacecraft such as to be capable of being rotated while remaining perpendicular to the sun direction. This known configuration is illustrated in FIG. 1 which schematically depicts an exemplary satellite 10. The payload and service module is designated by numeral 11 and the solar arrays are designated by numeral 12. The solar arrays 12 are mounted so as to be capable of being rotated about their longitudinal axis in the direction of the arrows 13 while remaining perpendicular to the sun direction. The module 11 is equipped with an earth sensor 14 which provides two-axes attitude information in pitch and roll. The missing yaw information requires the use of a momentum wheel having its momentum vector perpendicular to the orbital plane.
The known configuration has the following typical disadvantages:
(1) The earth horizon is a target with limited accuracy. Now some missions may demand pointing accuracies beyond the capability of infrared horizon sensors. Using RF earth sensors is a complex alternative which needs further development. In addition, whatever earth sensor may be disturbed by irregularities and by the sun and the moon as well.
(2) The presence of solar panels on the north and south faces of the satellite results in several disadvantageous consequences. First, the thrust for the correction of the north/south direction on a OTS satellite for instance requires two thrusters to be installed, for one sole thruster cannot fire through the center of gravity of the satellite. Second, said pair of thrusters may produce significant disturbing torques. Third, the north and south faces are obstructed and consequently their surfaces badly work as heat radiation areas.
(3) In transfer orbit operation there is required a special 3-axes stabilization equipment of the same type as that required for geostationary orbit.
(4) In case of a temporary breakdown of the attitude control system, the spacecraft is prone to flat spin.